Follow-up type fluid servomotor



March 2, 1954 H. e. CONWAY FOLLOW-UP TYPE FLUID SERVOMOTOR 5 Shet's-Sheet 1 Filed Feb. 25, 1949 m \M N k MI I lining:

MN g March 2, 1954 CONWAY I 2,670,715

FOLLOW-UP TYPE FLUID SERVOMOTOR Filed Feb. 23, 1949 3 Sheets-Sheet 2 9 5 1 I \A g a? Imam March 2, 1954 1-1.0. CONWAY FOLLOWUP TYPE FLUID SERVOMQTOR 3 Sheets-Sheet 5 Filed Feb. 25, 1949 QM E Patented Mar. 2, 1954 Hugh d ahami lo w en" .er, England, Laesignor to British Messier. 1L un ted, Gloucester,

ngland,-aj B x-itish company I I Applieatiflfl :Eebruarr :23; lacs, serial-asp. armor Qlaims priority, application GreatgBritain {February 23 i958 This invention comprises improvements in fluid-operated servo-motors and is particularly directed to servo-motors-of wthe riistonand cylinder type whereinthe distribution .of :pressure fluid to the opposed faces of ;the;piston-is.igovr ernecl by a servo-valve, movement of'iwhichcontrols the direction of motion of the piston.

The use of such .a servo-motor associatedrwith a servo-valve is well-known and in particular widely employed in hydraulic flying controls for aircraft, being primarily designed to :enablethe pilot of a large aircraft toiiyathigh speed, when th efforts required to move-thecontrol surfaces are greaterthan he can convenientlyexert-manually. In previous installations the flying-control servo-motor or jack and the-governing .-servo valve manually operated by the apilot have been separate units connected by 1condui ts for the passa e of the working fiuid and-a valve installed in this manner is susceptible ltd-leakage and is difiicult to protect againstthe entry f, -.d:irt.

The present invention contemplates the Elocation of the servo-valve withinthe pistoneitself with an operating member extending therefrom to the exterior of the jack. 1

A jack or servo-motor :accordingto the invention presents definite advantages-over other systems so farproduced in that external valve connections and leak paths to atmosphere areeli inated and the valve may be protected tron dirt far more easily thus providingone of-the fundamental requirements for .long life. Also the .installation and mechanical linkage 1 @much simpler and any developments whieh leadtoe simplification of .aircraft controls is of paramount importance. 7

.Such a servo-motor is particularly suited {for use as a hydraulic jack for operating aircraft flying control surfaces and for this service the body of the jack is locked to the aircraft structure and the piston rod is coupled to -zthe movable flying control surface while the-pilots control is connected to the lever arm to operate the valve.

These and further features .of the invention will become apparent from the following description which is given by way of ex mple .of tone embodiment of the invention in a practical iforrn applied to the control of aircraft flying control services, references being -made to the accom- De yi g drawings in which:

Figure .1 is a longitudinal licrizonta'lx-seotion through a jackin accordance with atheiinuentioni Figure 2 is a side elevation .offthe rconnection of a control lever tothe sack-piston rod; 7

worksia piston 42 operating upon a hollow piston rod The cylinder II has a head M which carries .ears' i=5 pierced at 11:6 to provide eyes for attachment 1110 an anchorage which may be a ifi-xed part of an aircraft. At the other end of :thecylinder Ii -is ya head 11 which contains astufiinggland -ilausurrounding the rod I3. The head H hasapipe connection I9 in the side for connection to :a high pressure hydraulic supply. The connection l9 opensthrough .a port.20;into

the interioriof the cylinder I I .around the piston rod: 43 1 and .tends to urge the piston 12 normally inwards, that i-s teward the head 14. Within the piston 12 :is ailinerzl containing ;a:b,ore, coaxialawith the :pist0n,.-in which works a pistonnah/e 22. The piston-valve "22 and associated parts zcanqbe more readily seen in the detail,

Figure 4-.of the drawing. Aport :23 pin the piston ail-admits fiuidunderpressure from the space aroundythe piston rod -:I3 tea-passage 24 in the Y piston-.1 2 and thence to a port .25 in the liner 2-;

2.4. Thezpistonevalve-H controls a port 26 opening'ion :to a passage '21 in the-piston [2 which leads :to the space between the .piston and the f head lil. The. portion .ZBofthe piston-valve 212 which :normally has .opposite the said port is made of the same diameter as the bore of the 'linerz2'l and-of the same length in an axial-.direc- .tion-.-as the mouth of the port 26 on the inner side .of the liner. .On each side of the port v26 j: thegpiston -valve .22 :has portions of reduced di- .5 ameter and lbeyondzthe portions of reduced .di- 1 ameter it has guided portions 29, i 30 which are ofctheisame idiameter as-the bore of the liner and which serve to keep the operative portion 28.. of the waive centralised .in the bore notwithstanding the .great'diiference of pressure which may at itimes exist around theuvalve between the ,pont l-iand the port .26. It will be appreciated that on aircraft 1 the hydraulic pressure may he of the order-of 2,000 "lbs. per square inch and that if any appreciable portion of the enlarged section 2 8 f' the valve =22 were in contact with .the linervzl ithis pressure-:would tend a hollow bore 32 within the valve and the hollow bore extends through the valve to a port 33 which communicates with the hollow space 34 within the hollow piston rod I3. The space 34 extends through the piston rod to a pipe connection 35 on the end of the piston rod outside the stufiin gland I8 which pipe connection can be coupled by a flexible pipe to a sump, that is to say to a fluid reservoir at atmospheric pressure to which the hydraulic operated fluid can be exhausted. A filter gauze 36 of hollow cylindrical formation is provided within the piston rod I3 and is held distended by a spring 31 (Figure 1).

It will be seen that if the valve 22 is moved to the left from the position shown in Figure 4 the space between the piston I2 and the head I4 of the servomotor will be connected by way of the ports 3|, 33 and space 34 to exhaust and the hydraulic pressure between the head I1 and the piston I2 will force the piston rod to move to the left. If the valve 22 on the other hand is moved to the right from the position shown in the figure the exhaust will be cut oh and the space between the piston I2 and the head I4 will be connected by way of the ports 23, and a port 26 to the hydraulic pressure existing around the piston rod I3 and as the area of the piston which lies to the left as viewed in Figures 1 and 4 is greater than the annular area surrounding the piston rod IS, the piston and piston rod will be forced to the right. In the central position a state of balance will be set up, the leakage between the edges of the portion 28 of the valve serving to maintain an intermediate pressure to the left of the piston which will balance the full pressure existing to the right of the piston.

The valve 22 is controlled by an operating rod 38 which extends through the hollow piston rod I3 past the pipe connection to the exterior as indicated at 39. The piston rod I3 is here forked into two branches 45, M and the fork-ends surround ball races 42 in which rock two side members 43, 44 forming part of a control lever 45. These parts are best seen in Figure 3 of the drawing. The ball races 42 are large enough in internal diameter to permit the operating lever branches 43, 44 to be drilled eccentrically to receive a bush 46 forming a bearing for a pivot pin 41. The centre of the pin 41 is above the axis of the ball bearings 42 as viewed in Figures 2 and 3 of the drawing and therefore movement of the lever to the right in Figure 2 will carry the pin 41 with it to the right. As can be seen in Figure 2 of the drawing the fork arms 40, 4| of the piston rod I3 are off-set downwards where they surround the ball races 42 and the amount of this off-set is sufficient to bring the axis of the pin 41 into line with the centre of the piston rod. The operating member 38 of the servo-valve is connected at 39 to a forked head 48 which lies between the arms 40, 4| of the forked head of the piston rod and the forked head 48 has fork arms 49, 50 which work on the bush 46 surrounding the pin 41. Therefore movement of the lever 45 to the right in Figure 2 will move the valve 22 to the right. This causes the piston I2 and piston rod I3 to move to the right and as soon as the movement equals the movement of the lever the valve is closed again and the movement stops. The same applies if the lever is moved to the left. Thus a servo action is obtained.

The lever sides 43, 44 extend below the ball races 42 and the fork arms 46, 4| also extend below the races and carry a pin 5|, the ends of which work in horizontal slots 52 in the bottom end of the lever. The pin limits the lateral movement of the lever.

- The pin 41 is extended beyond the bush 46 at each side and carries L-section washers 53 on which work suspension links 54. The suspension links 54 are bolted together by a bolt 55 below the lever 45 and they extend downwardly to a pivot pin on the aircraft (Figure 6). They serve to guide the movement of the forked end 40, 4| of the piston rod I3. Upon the bush 46 is a central ball race 56 which lies between the fork arms 49, 50, and surrounding the ball race 56 is an eye 51 of a connecting member 58 which has a screwed shank 59. The screwed shank 59 is adapted to be connected to any element which the servomotor. may be installed to operate, for example the flap I59, Figure 6, operated by lever I66.

Referring now to Figure 5 this shows parts which in general are the same as corresponding parts of Figures 1 and 4 and are similarly numbered so that detailed description is unnecessary. The difference is that the piston-valve 22 instead of operating with the central land 28 to control both inlet and exhaust is provided with an enlarged portion or land 50 at one end to control the admission of pressure fluid from a port 6| in the liner 2! to the space around the central portion of the piston valve and with an enlarged portion 62 at the other end which cooperates with the end of the bore of the liner 2| to control exhaust. The intermediate portion of the piston-valve between the enlarged portions 60, 62 is of smaller diameter to permit the passage of fluid and is provided with two guide portions 63, 64. The guide portions 63, 54 are a close internal fit in the liner 2| but they are grooved at intervals around their periphery in a longitudinal direction to permit the passage of the hydraliuc fluid to a port 65 in the center of the liner and thence by a passage 66 to the space lying to the left of the piston I2. The valve is maintained concentric with the bore by the portions 63, 64 and the enlarged portions 60, 62, not being normally entered in any part of the bore of the liner 2i which is subject to pressure, do not tend to cause sticking of the valve. The port BI is connected by a passage 6! to the pressure space surrounding the piston rod 3.

The amount of feel which the pilot requires in lever 45 can be adjusted to suit any requirement by varying the length of the lever.

Referring to Figure 6, the control lever 45 is shown connected by a rod I45 to an operator's control handle I46. Hydraulic pressure is continuously supplied at H! and at 35 the outlet is continuously open to exhaust. In operation, if the control lever 45 is moved to the right, as viewed in the drawing, the valve 28 is moved to the right. This is because the control lever 45 pivots about the center (indicated at 42 in the drawing) of the ball races on which the lever 45 is mounted and thereby carries the pin 41 to the right. The result is that the valve 28 opens communication between passage24 and passage 21 and thereby connects the space in cylinder H which is to the right of piston 12 to the space which is to the left thereof. As already explained, this causes the piston rod E3 to move to the right and the controlled element 159 is thereby actuated. When movement of the lever 55 by the operator ceases, it closes the valve 28 and movement of the element 159 ceases. In the course of the whole movement, as will be observed from the drawing, the operator has to maintain pressure on the lever as which is proportional to the resistance to movement of the element I59 because the force required to move the element I59 is applied to the element 59 by the piston rod 13 at the point 42 of lever 45 and is transmitted by the lever to the element 59 through the pin i'i. As the pin 4? is at a diiferent center from the center 42 about which the lever 45 turns, there is a reaction on the end of the lever which the operator can feel at the handle. In other words, he has the feel of the force necessary to move the controlled part. As soon as he ceases to push on the lever 45 the piston rod I5 catches up with the movement and the valve 28 closes the passages 24, 27, thus holding the controlled element l 59 in the position which it has attained.

If the operator wishes to move the control element I50 back again he moves the lever M5 in the opposite direction which opens the passage 21 to the space within the piston rod [3 and thus to the exhaust 35 allowing the piston [2 to move to the left and follow the movement of the lever 45 until it catches up again. In so doing the operator can feel the force exerted on the controlled element 59 for the same reason as "already explained, namely, that the center ll where the force is exerted on the controlled element is not at the same point on lever 35 as the pivotal center 52 of the lever Thus a power movement is effected in both directions although there are only two connections, [9, 35, to the servomotor and owing to the extremely small movement required to unbalance the pressure by flow of fluid through valve 28 there is no back-lash, that is to say the movements of the control surface follow the movements of the operating lever with great closeness.

I claim:

1. In a servo-motor the combination of a motor cylinder having means for attachment to an aircraft, an assembly comprising a piston and piston-rod of which the piston fits the cylinder and the rod passes through one end of the cylinder and contains an exhaust passage, a sliding control valve within the assembly, parts to said 6 valve which in one position thereof open connection between opposite sides of the piston and in another position thereof open connection between the side of the piston remote from the pistonrod and the exhaust passage, a fluid supply connection to the end of the cylinder which surrounds the piston-rod, a lever pivoted on the outer end of the piston-rod, a valve-operating rod operatively connected at one end to the valve and at the other end to the lever near to its pivot and an operative connection from a point on the lever close to its pivot to the load.

2. In a servo-motor the combination of a motor cylinder havin means for attachment to an aircraft, an assembly comprising a piston and piston-rod of which the piston fits the cylinder and the rod passes through one end of the cylinder and contains an exhaust passage, a fluid supply connection to the end of the cylinder which surrounds the piston rod, a sliding control-valve within the assembly, parts in the assembly controlled by said valve which in one position thereof open connection between opposite sides of the piston and in another position thereof open connection between the side of the piston remote from the piston-rod and the exhaust passage, a lever pivoted on the outer end of the piston-rod at a point offset from the center line thereof, a valve-operating rod pivoted to the lever at a point approximately on said center line, an operative connection also approximately on said center line from the lever to the load, and a supporting link pivoted at one end to the lever and at the other end to a point of support on the aircraft.

HUGH GRAHAM CONWAY.

References Cited in the file of this patent UNITED STATES PATENTS FOREIGN PATENTS Country Date Great Britain Mar. 2, 1931 Number 773,365 2,152,08i 2,227,273 2,424,901 2,437,536 2,449,400 2,457,721 2,462,994 a l-72,547 2,503,956

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